Earnings per Share (Summary of Basic and Diluted Earnings per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Earnings per Share [Abstract]
Net income (loss) available to common stockholders	$ 4,082		$ 4,198
Weighted average shares outstanding-basic	31,294,488		29,016,774
Net income per share-basic	$ 0.13		$ 0.14
Net income	$ 5,037		$ 5,328
Weighted average shares outstanding-diluted	39,209,226	[1]	36,889,474	[1]
Net income per share-diluted	$ 0.13		$ 0.14

[1] Includes 7,317 Class A and Class RS units, 436 “in the money” value of Class O units on an “as if” converted basis and 216 “in the money” value options to purchase shares of Class A common stock on an “as if” converted basis as of the three months ended March 31, 2015. As of the three months ended March 31, 2014, this amount includes 7,797 Class A and Class RS units, 24 “in the money” value of Class O units on as “as if” converted basis and 52 “in the money” value options to purchase shares of Class A common stock on an “as if” converted basis.